The present invention relates to a method for manufacturing a liquid crystal display device.
FIG. 5 is an explanatory view showing a liquid crystal panel of a conventional liquid crystal display device, and FIG. 6 is a sectional view taken along the line A--A in FIG. 5. In the drawings, numeral 1 denotes a pair of opposed transparent insulation substrates composed of transparent insulation substrates 1a and 1b. Numeral 11 denotes an alignment layer formed on the transparent insulation substrates 1a and 1b; numeral 10 a seal pattern comprising a sealing material for adhering a pair of opposed transparent insulation substrates 1 and determining an injection area of liquid crystal; and numeral 3 a liquid crystal injection hole which is an opening of the seal pattern 10. Numerals 16a, 16b, . . . , 17a, 17b, . . . denote respectively display electrodes extending under the sealing material to a substrate terminal 4. The substrate terminal 4 is formed on either one la of a pair of transparent insulating substrates for transmitting a signal to the display electrodes 16, 17 from outside, and is separated from the pixel area through the sealing material. Numeral 5 denotes a cutting position of the transparent insulation substrate 1a, when forming a panel, on which the substrate terminal 4 is formed, and numeral 6 denotes a cutting position of the other transparent insulation substrate 1b when forming a panel.
Next, the manufacturing process of the conventional liquid crystal display device is explained.
First, an alignment layer 11 is transferred to the surfaces of two transparent insulation substrates 1a and 1b to be calcined, on at least one of which there are formed electrodes and a substrate terminal 4. Next, on either one of the transparent insulation substrates 1a and 1b, a sealing material is applied to form a seal pattern 10 having a liquid crystal injection hole 3. Next, the two transparent insulation substrates 1a and 1b are oppositely placed and pressed on each other, and the sealing material is cured to form a pair of opposed transparent insulation substrates 1. Thereafter, predetermined panel assembly steps are carried out, the adhered pair of transparent insulation substrate 1a, 1b, are cut at the substrate cutting positions 5 and 6, and liquid crystal is injected from the liquid crystal injection hole 3 to form a liquid crystal panel.
Conventionally, the seal pattern 10 is formed on the surface of either one of the pair of transparent insulation substrates 1 by screen printing method or dispenser method.
According to the screen printing method, a substrate is held under the screen plate comprising a mask having an opening of a predetermined shape and is rubbed with a roller with a sealing material being adhered to the surface of the roller over the screen plate to apply the sealing material to the substrate corresponding to the opening of the mask to form a seal pattern. The principle of this method is to use a sealing material in place of an ink and a substrate in place of paper in an ordinary mimeograph printing.
According to the dispenser method, after a sealing material into which a predetermined spacer is kneaded is filled in a syringe, the syringe is set on a dispenser, and the sealing material filled in the syringe is discharged by mainly utilizing a pneumatic pressure. The space between the substrate and the discharge part is precisely controlled, and a predetermined amount of sealing material is applied in a predetermined pattern by computer control to form a seal pattern.
As described above, with respect to the method for forming an area into which liquid crystal is injected in a liquid crystal display device and forming a seal pattern for adhering a pair of transparent insulation substrates, there have been conventionally proposed several methods, but they are not effective. For example, in a screen printing method, since the screen plate is directly brought into contact with the alignment layer formed on the transparent insulation substrate, there has been a problem to cause defective orientation due to stain or damage of the alignment layer.
Further, according to the dispenser method, due to discharge of the sealing material by pneumatic pressure, the discharge amount is not stabilized so that the shape of the seal pattern is not uniform at the application starting position and application ending position. That is to say, at the application starting position, because of the necessity to elevate the discharge pressure to a pressure level at which the sealing material can be applied, the actual application starting position is displaced from the application starting position targeted by the seal pattern. Alternatively, by allowing the dispenser for applying sealing material to stand at the application starting position for a predetermined duration of time, delicate fluctuation of pressure occurs to cause dropping of sealing material from the syringe, thereby giving large initial discharge amount to make the shape of the seal pattern at the application starting position larger than the target size. At the application ending position, due to the residual inner pressure in the syringe, there has been a problem that the application of the sealing material cannot be stopped at the application ending position.
For example, FIG. 7 is an explanatory plan view of the substrate in the case where an injection hole is formed on the substrate terminal, and FIG. 8 is a sectional view taken along the line B--B in FIG. 7. As shown in FIG. 7, when setting the application starting position 10a and the application ending position 10b of the seal pattern 10 at the liquid crystal injection hole 3, there arise the conditions where the seal pattern 10 at the liquid crystal injection hole 3 is not sufficiently formed to the substrate cutting position 6 or the sealing material projects to the substrate terminal.
In case that the seal pattern 10 for the liquid crystal injection hole 3 is not sufficiently formed to the substrate cutting position 6, as shown in FIG. 9, there is formed a gap 12 between the application starting position 10a of the seal pattern 10 and the substrate cutting position 6, so that a foam 14 might mix in the liquid crystal 13 from the gap 12 during injection of the liquid crystal 14 to cause a defective display of liquid crystal display device.
Further, when the sealing material projects to the substrate terminal 4, the cut piece 15 of the substrate adheres to the sealing material to make it impossible to remove the cut piece 15.
The present invention has been made to solve the problems as described above, and its object is to form a seal pattern capable of preventing defective injection of liquid crystal caused by inclusion of foam during injection of liquid crystal or defective cutting of substrate in the process of forming a liquid crystal display panel.